When I run iperf as a client on a CentOS 5 VM running under vmware, why do I see such high %si values in top? We have more experience running Xen and XenServer, and a almost identical centos install under Xen shows only ~0.5%si while running iperf. All tests run with 1Gb network, and the numbers we are getting from iperf are good/fine (900+ Mb).